Vehicle doors generally comprise a hollow structural unit or shell that is made of an inner sheet metal door panel and an outer sheet metal panel that are mated together and secured to each other along a mating periphery. In the past, the vehicle door was then completed by adding several parts to this hollow structural shell more or less individually.
In recent years, most vehicle doors have included a crash beam that extends across the length of the vehicle door to absorb side impact loads and thus improve passenger safety and crashworthiness of the vehicle.
Another recent trend in vehicle doors is modular construction where several door parts are preassembled into a module that is then assembled to the hollow structural shell as a preassembled module rather then a number of individual parts; the purpose of the modular construction being to facilitate assembly and reduce assembly cost. See for instance, U.S. Pat. No. 5,535,553 granted Jul. 16, 1996 to Brian H. Staser, Danny W. Figlioli and Daniel H. Forrest for a superplug vehicle door module.